1. Field of the Invention
The present invention concerns a universal type butterfly valve, that is a butterfly valve that can be assembled between any of the types of flanges manufactured in compliance with currently existing international standards, namely AFNOR, DIN, ISO, ANSI, AWWA, MSS, BS, JIS standards.
2. Description of the Prior Art
Generally, a butterfly valve comprises:
a body manufactured in one or several parts and including a central bore, two parallel radial faces in the middle of which the said bore opens and a transversal drilling at a right angle to the centerline of the said bore, PA1 a butterfly assembled so as to rotate inside the said body by means of at least one operating shaft inserted in the said drilling, and PA1 a sealing lining that cooperates with the said body and the said butterfly to ensure upstream/downstream tightness when the valve is in the closed position. PA1 external sealing through the compression of the part of the flexible ring that turns up on the radial faces of the valve, and PA1 mechanical coupling between the two pipe sections and the valve.
The invention more specifically concerns a butterfly valve in which the sealing lining consists in an elastomer flexible ring or sleeve, with a basically U-shaped section, the core of which lines the body bore and the lateral cheeks of which turn up against the radial faces of the body and ensure external sealing at the point where the valve is joined to the piping.
In this respect it should be noted that this type of valve is usually joined to the piping by means of two connecting flanges, each one of which features a radial face designed to be assembled tightly against a matching radial face on the valve body. To this effect, each one of these flanges displays a series of evenly laid out axial holes, through which pins or screws are inserted. Each pin or screw is threaded through a couple of matching coaxial holes on both flanges and is bolted at each end, in order to ensure both:
Moreover, in many types of valves, the cheeks of the sleeve partially fit into a circular recess provided in the matching faces of the body. In some valves, this recess comprises, outwards from the body bore, a radial surface axially offset from the said face, then an annular groove. In this case, at the radial surface of the recess the sleeve cheeks are slightly thicker than the depth of the recess and at their ends they are shaped as a tenon that fits into the said annular groove.
This pattern ensures that the sleeve is properly anchored to the body and at the same time restricts the compression exerted on the cheeks to suit the level of sealing desired, in the understanding that this sealing is obtained when, owing to the stress induced by bolting the pins, the radial faces of the flanges are pressed against the radial faces of the valve body.
In this type of assembly, the valve body is centered on the flanges by means of the pins or screws. To this effect, a central rib (or two lateral ribs if applicable) may be provided on the perimeter of the valve body, in which axial holes or notches are drilled, through which the pins or screws are threaded.
However, the present situation is that for the same type of valve, the inner diameter of the flanges, the angular position of the holes provided in the flanges for the pins or screws, the distance of these holes to the flange centerline and the diameter of the holes are all different according to the various standards currently in force.
These differences in flange shapes require specific ranges of valves designed to match each type of flanges, and this particularly relates to the position and size of the holes or notches through which the pins or screws must be inserted.
In addition, it appears that in butterfly valves of the type described above, the compression of the sleeve cheeks by the radial faces of the flange causes a displacement of the elastomer which results in a corresponding variation of the thickness of the core of the sleeve on which the butterfly bears. The quality of the upstream/downstream tightness of the valve, as well as the operating torque are therefore affected by this creep effect.
As a result, the use of flanges complying with different standards, and therefore with different inner diameters, results in a variation of the tightness and operating torque features of the valve, owing to the volume variation induced by the compression of the elastomer.